This invention relates to postcards having hidden messages.
Hager (Swiss Pat. No. 32728, 1905) describes a postcard having a single sheet of carbon paper held between two sheets. A third sheet is provided to allow a message to be written onto the sheet held against the marking side of the carbon paper.
Jaubert (French Pat. No. 07695, 1973) describes a card having two sheets with a single sheet of carbon paper held therebetween. The carbon paper hides a message from view.
Weinschenk (U.S. Pat. No. 2,365,789; 1942) describes a postcard upon which a typewritten message can be made without removing the card from the typewriter. A single sheet of carbon paper is placed between the card and a second sheet of paper.
James (U.S. Pat. No. 2,831,707; 1955) describes a check and envelope assembly between which a sheet of carbon paper may be placed to reproduce any written material, and thus aid in record keeping.